It is known for example from my U.S. Pat. No. 3,277,834 that a piston shoe is inserted between the actuator of the piston stroke and the respective piston in radial piston type fluid handling devices. From the said patent it is also known, that the piston shoe is provided with a pivot portion of part-cylindrical configuration in order to swing or pivot in a respective bed of the piston. Fluid pressure balancing pockets were associated to the pivot portion in order to reduce friction between the piston and piston shoe.
Those piston shoes have operated satisfactorily in the past. However, in newer times the rotary velocities of such devices is increased and the pressure in fluid is also increased in radial piston type fluid handling devices. Thereby it appeared, that the total efficiency decreased, when the rotary velocity or pressure was increased. According to this invention it has now been discovered that to a large extent the loss of efficiency came from a too narrow size of the bearing face of the piston shoe's pivot member and by an unsuitable configuration of the ends of the pivot portion and of the location and size of the fluid pressure balancing recess associated thereto. These drawbacks are overcome according to this invention thereby, that the end face of the part-cylindrical pivot portion of the piston shoe becomes formed as a part-cylindrical face with a radius of a slightly shorter size than the radius of the associated piston is. The fluid pressure balancing recess becomes extended in size and its walls are configurated to conform substantially to the invented end face configuration, but leaving enough space to form a suitable sealing face. Further improvements consist in an inclination on the piston-most portion of the end-portions of the pivot member or in the increase of the radius of the bearing face of the pivot portion.